Background: The low molecular weight heparin (LMWH) Tinzaparin (T) is used as an anticoagulant in haemodialysis. For the achievement of the proper anticoaggulant it is required the quantitative determination of T levels and is expressed as anti-X efficacy. The aim of this study is to check the effectiveness of T as a bolus dose prior to haemodialysis.Patients and Methods: A total of 54 patients have been examined and divided into 2 groups according to their weight. The 1st group (45 patients) received 3500 I.U. of T and the 2nd group (9 patients) 4500 I.U. of T. Those patients with body weight (BW) over 70 kg received 4500 I.U. At the beginning and at the end of the third hour, blood has been taken for the quantitative determination of the anti-X efficacy, fibrinogen, prothrombin time (PT) and partial thromboplastin time (?�?T). The results have been correlated with I.U. of T per kg b.w and between them. The anti-X efficacy in plasma has been analysed at 405 nm using chromatometry (STAGO, Rotachrom HBPM / LMWH).Results: The anti-X efficacy at the third hour fluctuated for the first group between 0.12- 0.82 I.U. / ml with mean value 0.52?0.17 I.U. / ml and for the second group between 0.30-0.97 I.U. / ml with mean value 0,53+0,21 I.U. / ml. Low values (0.07 and 0.12 I.U. / ml) have been found in two patients of the first group. After the increase of the providing dose of T to 4500 I.U., the anti-X efficacy has been increased to 0.32 I.U. / ml and to 0.36 I.U. / ml respectively. The dose in I.U. T per kg BW fluctuated in the 1st group between 36.45- 92.10 with mean value 57.97? 14.34 and in the 2nd group between 52.32- 95.74 with mean value 68.97? 14.75. In most of the patients a prolongation of the ?�?T has been found. It has been observed that there was no correlation between fibrinogen, PT, ?�?T and I.U. T per kg BW However, in the total of the patients (1st and 2nd group), a small but statistically significant correlation (r = 0.61, p<0.05) was found between I.U. T per kg BW and the values (I.U. / ml) of anti-X efficacy.Conclusions: The initial bolus dose of T is satisfactory and with a mean value of 60 I.U. of T per kg BW achieved a mean anti-X efficacy of 0.52 I.U. /ml which is adequate in order to have suitable anticoagulant effects without unnecessary side-effects.